1. Field of the Invention
This invention relates generally to a method for fabricating a regulator valve controlled by a direct acting solenoid located in a machined main control casting for an automatic transmission.
2. Description of the Prior Art
An automatic transmission includes a hydraulic system for regulating fluid pressure and hydraulic fluid flow in various lines connected to components of the transmission. The system includes a regulator spool valve packaged in a main control casting, which is machined at a transmission production plant. The casting, preferably of an aluminum alloy, is usually referred to as a valve body. The components of the system are assembled in the valve body.
A solenoid-actuated shift valve controls pressure communicated from the valve to a clutch or brake whose state of engagement and disengagement determines the gear in which the transmission operates. But the dimensional tolerance stack-up in most valve body castings is too large to permit use of a practical integrated electromagnet and achieve required flow and pressure regulation accuracy.
Transmissions with direct acting solenoids require a method to provide hydraulic pressure to clutches and brakes for high torque operating conditions such that the pressure can be delivered independently of the control pressure range suitable for shift control.
A need exists in the industry for a method for machining a valve in a valve body, such that the dimensions of certain features of the valve and the related tolerances are ultra-precise. Preferably the critical features, such as a groove and a face surface, are machined concurrently in a single operation with processing equipment that employs a minimum quantity lubrication machining process.